Functionally important binding site for a volatile anesthetic in a voltage-gated sodium channel identified by X-ray crystallography

Volatile general anesthetics are used for inhalational anesthesia in hundreds of millions of surgical procedures annually, yet their mechanisms of action remain unclear. Membrane proteins involved in cell signaling are major targets for anesthetics, and voltage-gated ion channels that mediate neurotransmission, movement, and cognition are sensitive to volatile anesthetics (VAs). In many cases, the effects produced by VAs on mammalian ion channels are reproduced in prokaryotic orthologues, providing an opportunity to investigate VA interactions at high resolution using these structurally simpler prokaryotic proteins. We utilized the bacterial voltage-gated sodium channel (VGSC) NavMs from Magnetococcus marinus to investigate its interaction with the widely used VA sevoflurane. Sevoflurane interacted directly with NavMs, producing effects consistent with multisite binding models for VA actions on their targets. We report the identification of one of these interactions at atomic detail providing the first high-resolution structure of a VA bound to a voltage-gated ion channel. The X-ray crystal structure shows sevoflurane binding to NavMs within an intramembrane hydrophobic pocket formed by residues from the voltage sensor and channel pore, domains essential for channel gating. Mutation of the dominant sevoflurane binding-site residue within this pocket, and analogous residues found in similar sites in human VGSCs, profoundly affected channel properties, supporting a critical role for this site in VGSC function. These findings provide the basis for future work to understand the role of VA interactions with VGSCs in both the anesthetic and toxic effects associated with general anesthesia.